1. Field of the Invention
This invention relates to a printing apparatus for depositing a liquid composition on a surface. In particular, depositing of a liquid composition containing an organic semiconductor material on an backplane. More particularly, a nozzle assembly having a throttling plate and variable accumulation volume to mitigate pressure variations arriving at the inlet to the nozzle assembly. The mitigation of pressure variations results in improved print quality and performance of the organic semiconductor material in an electronic device.
2. Description of the Related Art
An electronic device can include a liquid crystal display (“LCD”), an organic light-emitting diode (OLED) display, or the like. The manufacture of electronic devices may be performed using solution deposition techniques. One process of making electronic devices is to deposit organic layers over a substrate by printing (e.g., ink-jet printing, continuous printing, etc.). In a printing process, the liquid composition being printed includes an organic material in a solution, dispersion, emulsion, or suspension with an organic solvent, with an aqueous solvent, or with a combination of solvents. After printing, the solvent(s) is(are) evaporated and the organic material remains to form an organic layer for the electronic device.
OLED devices utilizing one or more layers of organic semiconductor materials laminated between other supporting layers and sandwiched by two electrodes are used in many different kinds of electronic equipment.
Each organic semiconductor material is carried in a liquid composition. During manufacture of a device each liquid composition is dispensed from a dedicated nozzle assembly. The nozzle assemblies are grouped in nozzle sets, with one nozzle in each set dispensing a particular color of ink. Each nozzle assembly dispenses liquid and deposits that liquid along a longitudinal lane that extends across a backplane of the device. The nozzle assemblies in each set continuously dispense a liquid composition into a respective lane. The nozzle assemblies can be located within a printhead, and the printhead travels in a linear path in a first or forward direction, in addition to a second or reverse direction, while printing the liquid composition on the backplane.
The individual nozzle assemblies for each particular color in each nozzle assembly set are supplied as a group from a common manifold itself supplied from a suitable liquid composition supply source, or supply reservoir. The supply reservoir for each particular color is usually implemented as a communal reservoir. The supply reservoir may either directly hold a supply of liquid for the nozzle assemblies, or may hold a secondary container, such as a sealed pouch containing the particular colored liquid composition.
Liquid printing can be conducted in either non-continuous or continuous operation as disclosed in the prior art. Any pressure pulses in a non-continuous system are isolated from the dispensing of the liquid composition. One example of non-continuous liquid printing would be ink-jet printing where discreet droplets of liquid are ejected from a nozzle. Localized impulse to produce the liquid droplet is distinct and segregated from the liquid supply source, manifold, and feed tube. The arrangement in a continuous printing method does not enjoy the isolation of pressure pulses of the ink-jet printer.
Within the continuous printers, one option to eliminate or mitigate pressure pulses acting on the liquid composition is to arrange a stationary printer and move the target substrate upon which the liquid composition is deposited. Another option is to locate the manifold in close proximity to the nozzle to minimize pressure pulses traveling along the feed tube. For a moving printhead one solution has been to supply a length of tubing, having a first diameter, to act as a capacitive element to slow the liquid composition before entering the printhead. Another solution is to supply an additional length of tubing, having a second diameter, between the supply of tubing and the printhead, where the second diameter is less than the first diameter. The first length of tubing acting in a capacitive fashion while additional length of tubing acts in a resistive fashion, hence, the fluidic equivalent of an CP (Capacitive-Resistive) electronic circuit.
However, the above solutions have not met the required level of printing uniformity required for organic electronic devices. In particular, the pressure variations continue to plague the printing operations by causing at least one type of non-uniformity referred to as stitching, where heavier and lighter print deposition on the intended deposition surface result in ultimate degradation of final organic electronic devices.
In view of the foregoing it is believed additional improvement is required to improve organic electronic devices.